The present invention relates to an inspection method for foreign substances or defects produced in fabricating an LSI and a liquid crystal substrate and an apparatus therefor.
With the downscaling of semiconductor devices, the size of defects or foreign substances on a fine pattern that is an inspection object is a few nanometers or less. Since the size of defects or foreign substances that are objects for detection becomes thus smaller, reflected, diffracted, and scattered light from these defects and foreign substances are really weak, and it is difficult to optically detect them. Thus, such a method is proposed in which plural images are acquired under pluralities of lighting conditions and detection conditions (detection orientation, detection elevation angles, and polarization detection) and these images are used to improve defect detection sensitivity, using the fact that reflected, diffracted, and scattered light from defects or foreign substances depend on the luminous light conditions (lighting orientation, lighting elevation angles, wavelengths, and polarization).
For inspection methods for defects or the like produced on a semiconductor wafer using the method above, there are methods described in Japanese Patent No. 4,001,653 and Japanese Patent Application Laid-Open Publication No. 2008-096430.
The method described in Japanese Patent No. 4,001,653 describes a defect inspection method and an apparatus therefor in which in order to find defects on inspection points on a first pattern on a sample, a reference is made to at least one known inspection response of a second pattern in the same design. Such a technique is described that in inspection, it is important to use equivalent observation points on the first and second pattern on the sample, at least one search is performed to produce at least two inspection responses, these two responses (typically, response signals from a dark field and a bright field) are separately detected by a photoelectric scheme and separately compared with each other, and differential signals are individually formed (between the first and second pattern). Namely, first and second responses on the first pattern are detected, and the results are individually compared with two responses from the same corresponding inspection points on the second pattern, and first and second differential signals between the responses are formed as the results. The differential signals individually formed are processed into data in order to determine a first pattern defect list collectively. More specifically, these first and second differential signals are collectively processed into data to determine a unified first pattern defect list. Alternatively, the first pattern defect list is subjected to data processing later. Known, harmless false defects observed on a sample surface are then extracted and removed. On the other hand, such known, harmless false defects are provided to a user for reference. A variety of inspection searches are added to increase inspection responses, and two optical responses or more are obtained for processing. Thus, inspection accuracy is further improved. In addition to this, it is described that for a transparent sample, a photoelectric detector is provided on the rear side of the sample and inspection responses of transmitted light are collected, so that the accuracy of the pattern defect list can be further improved, and defects buried in the inside of the sample can also be found. However, there is no specific description to obtain two responses.
There are problems in that the distributions of reflected, diffracted, scattered light from a defect on a semiconductor wafer are varied depending on the size and shape of the defect and on the surface topology of the wafer and the defect detection performance of a single detector depends on types of defects. The method described in Japanese Patent Application Laid-Open Publication No. 2008-096430 provides a method of addressing the problems in which light is applied to a semiconductor wafer obliquely to the normal of the wafer, reflected, diffracted, and scattered light from the wafer are detected in almost the entire hemispherical area as the target object is placed on the bottom, and the lights are used to detect and distinguish defects. The method further describes that similar polarized light or different polarized light is applied from plural directions at the same time, and plural polarization components are individually detected to reveal defects using the difference in the polarization characteristics between defects and noise.
When the size of an inspection object is a few nanometer size, the polarization characteristics of the inspection object are greatly varied depending on slight differences in the characteristics of the micro structure and medium of the inspection object. Consequently, the states of polarization of lighting and detection are appropriately selected to expect the improvement of defect detection sensitivity.
However, the optical defect inspection apparatuses according to the conventional techniques use the schemes of processing plural images obtained under pluralities of lighting conditions (lighting orientation, lighting elevation angles, wavelengths, and polarization) and detection conditions (detection orientation, detection elevation angles, and polarization detection). However, the polarization of lighting, which is one of the conditions, is not always efficiently used.
In order to efficiently use the polarization characteristics of an inspection object, it is necessary that light in the same direction and with the same angle of elevation and the same wavelength but a different polarization in polarized light be applied and differences between reflected, diffracted, and scattered light from the inspection object due to polarized light be observed. When this is performed in the conventional techniques, plural measurements, in which polarized lights are switched, are necessary to increase a detection time period that is an important specification of the inspection apparatus.